chore(deps): ignore major toolchain updates

[christopherjnelson]

Summary

• ignore major Dependabot updates for @types/node, eslint, and typescript
• keep @types/node aligned with the Node 24 runtime
• require intentional compatibility migrations for ESLint and TypeScript majors
• preserve monthly grouped routine updates, one open PR per ecosystem, security updates, and manual merge control

Root cause

After the dependency automation cleanup merged, Dependabot immediately recreated an incompatible grouped major update in #7. That PR moved Node types beyond the project runtime and introduced ESLint and TypeScript majors, producing a large lockfile rewrite and failing CI.

Impact

Routine non-major and security dependency automation remains enabled. Toolchain majors will be handled deliberately in dedicated compatibility migrations.

Validation

Local validation was not run, per repository instructions. The diff was inspected and contains only .github/dependabot.yml; normal GitHub CI is expected to run.